Preheat water to 158°F using a sous vide precision cooker.
In the meantime, place the pork shoulder in a large Ziploc bag or a sous vide bag.
Whisk all the ingredients for the marinade (except the fresh rosemary sprig if using) in a small bowl until well combined. Pour it over the pork. Shake gently until the marinade covers all sides of the pork.
Drop the fresh rosemary sprig into the bag. If using a sous vide vacuum bag, seal with a vacuum sealer or a hand pump, then slowly lower it into the prepared water bath. If using a Ziploc bag, leave it open and slowly lower it into the prepared water bath using the displacement method to let the water push the air out, then zip it up. Make sure that the pork is completely under the water-line.
Cover the sous vide container with plastic wrap to prevent the water from evaporating. Set timer for 24 hours.
Once the pork is done, transfer it to a cutting board, a large plate, or a baking sheet lined with foil. Shred the pork using two forks. Reserve the cooking juice for serving.
For a crispy top, insert the baking sheet under a preheated broiler and broil for 7-10 minutes until the top side of the pork is golden-brown and crispy. You may also sear the pork in a hot cast-iron skillet or a large nonstick pan, one layer at a time. No need to add any oil. (This step is optional but it’s highly recommended.)
Sprinkle freshly ground black pepper and serve the pork in tacos, burrito bowls, or sandwiches, or pair it with rice and vegetables. Drizzle the cooking juice on top if desired.